Tractor hydraulic system maintenance

The hydraulic system is a very important part of the agricultural tractor, as it is what makes most work with agricultural implements possible.

One of the main sources of power, responsible for high agricultural production with significant labor savings, is the agricultural tractor. Numerous implements and machines capable of carrying out the most different agricultural operations required in rural areas can be coupled and adapted to it.

Typically, agricultural tractors have, as a way of transmitting power, the drawbar, the power take-off (TDP) and the hydraulic system, consisting of the three-point hitch and remote control valve (VCR).

Implements and machines can have a coupling mounted, when linked to the three points of the tractor's hydraulic coupling system; semi-assembled, when tied to the two lower points of this coupling system; and drag, when coupled to the tractor's traction bar. In addition to these forms of coupling, the tractor can transmit power together with the PTO and remote control valve activated, depending on the implement's demand and tractor availability.

The function of the remote control valve (VCR) is to direct oil at high pressure, through hydraulic connections, to pistons and hydraulic pumps of agricultural machines and implements, to perform various functions such as moving shovels, blades, buckets and other sectors and parts of machines, in addition to driving hydraulic motors for spray pumps, product distributors, seeders, among other machines. The tractor's VCR system basically consists of couplers on the back of the tractor, control levers or buttons positioned on the tractor's operating platform, reservoir, pump, filters, control and relief valves and piping.

The hydraulic pump, driven by the tractor engine, circulates the hydraulic oil, feeding it from the tank that ensures continuous supply. The relief valve, present between the pump and the control valve, allows excess fluid to return to the reservoir. A control valve channels the oil according to the conditions imposed on the system, directing its direction or interrupting the flow. Finally, the cylinder will receive the circulating fluid and transform it into effective work when requested, extending or retracting. At this moment, the cylinder exerts a force proportional to its internal diameter and the hydraulic pressure of the oil, moving the attached object. There may also be a hydraulic motor, which, activated by a specific constant pumping valve, allows driving axles, among others.

In practice, this set is completed by piping, filters, connections and in more complex cases, incorporating other types of valves depending on the desired purposes. This creates an airtight system capable of withstanding certain operating pressures, transmitting a certain level of hydrostatic energy.

The couplers located on the tractor, or receptacles, are of the female type and allow quick coupling of male couplers located at the ends of the hydraulic hoses of agricultural implements. These connections are standardized, as recommended by ISO (International Standardization Organization) and SAE (Society of Automotive Engineers). The female and male couplers must have the same size and not show wear to allow perfect coupling without loss of pressure and oil. Agricultural tractors normally have two pairs of couplers, but more can be installed, depending on the characteristics of the tractor's hydraulic pump.

CONNECTING THE TERMINALS

Initially, the dust protections must be removed from the tractor couplers and the end of the hose, ensuring that the terminals are clean.

Before connecting the implement couplers to the tractor, it must be checked whether the implement hose is under pressure, if it is, the operator will not be able to join the male to the female – if he forces the coupling, he could even injure himself. with the fluid, which can escape during the connection attempt and penetrate the skin and eyes, causing serious injuries. To remove pressure from the end of the hose, you can press the male coupler to a non-metallic surface to move the check valve, located at its end, until you verify that no more oil comes out.

In some high pressure situations where this decompression is not possible, it is important to somehow relieve the pressure that exists in the hydraulic cylinder, removing the load on it, supporting or elevating the sector of the machine that is possibly causing the pressure in the hydraulic cylinder. hydraulic cylinder. Therefore, it is always important to decompress the system before uncoupling and keep the implement in a rest position where the hydraulics are not under pressure. It is also important to regularly observe the general condition of connectors, hoses and cylinders in search of physical defects, wear and leaks.

To connect the hoses, the end (male) must be firmly pushed against the coupler receptacle (female). The connectors have internal safety valves to prevent oil leakage in case of accidental disconnection. If this occurs, it is necessary to depressurize the system, clean the connectors and reinstall the hoses.

You must observe the implement hoses to determine which one should be used to extend the cylinder when the VCR levers are operated. If they are coupled invertedly, they must be uncoupled and inverted to the correct position.

REMOTE CONTROL SYSTEM

The remote control system can work with single-acting or double-acting cylinders. When using the single-acting cylinder, after coupling, the functioning of the system must be checked, paying attention to the hydraulic oil level – the volume of oil required to extend the cylinder must not cause the oil level to rise. hydraulic pressure drops below the dipstick.

The control lever, on some tractor models, has a floating position. To place the lever in this position, it must be moved fully forward, overcoming the resistance of the lever spring. In this position, the cylinder coupled to this terminal can extend or retract freely, similar to the situation of an implement that works in contact with the ground, following its irregularities without offering resistance to vertical movement. When you do not need the float function, you must place the lever in neutral to avoid accidental activation of the float.

Some implements have hydraulic motors, which require the valves to operate in a constant pumping position. This system is present on some tractor models or can be installed as an option.

To decouple the connections, it is necessary to first retract the hydraulic cylinder to protect its rod from damage if possible. Next, the hydraulic pressure in the hoses must be relieved, turning off the engine and moving the lever back and forth, until you notice that the cylinder no longer moves. After uncoupling, the terminals and their respective caps must be cleaned and the connectors covered to keep them clean.

SOME NOTES TO KEEP THE SYSTEM ALWAYS WORKING

Ricardo Ferreira Garcia, José Francisco Sá Vasconcelos Junior, UENF

Article published in issue 162 of Cultivar Máquinas.